Instructions
Upgrade your Chaoseater sword before beginning the battle to make your attacks as strong as possible. Lock onto Tiamat to keep her in your sights throughout the battle.
Run over and pick up one of the inert bombs lying on the ground as soon as the battle begins. Get as close to Tiamat as possible. Target Tiamat and throw the bomb at her, which causes the inert bomb to stick to her.
Click R3 to go into aim mode and aim at a torch. Select the torch as a target. Aim the target at the bomb on Tiamat and choose it as a second target.
Send your crossblade through the torch and on to Tiamat to ignite the bomb. Run to her and attack her when she crashes to the ground. Press the R1 button to dash away when she begins to get up.
Avoid Tiamat's attacks by dashing to the side when she swoops at you. She will rise up before each swoop, which will warn you of the attack. Dash away backward when Tiamat begins fighting from the ground each time she jumps up to avoid the shock wave that hits when she lands.
Continue fighting her on the ground, attacking her with your sword until Tiamat is finished. The battle will stop and turn to video format that shows you ripping off her wings and tearing out her heart.